The invention relates to an electrophotographic apparatus in which a toner image formed on a photosensitive member as a result of developing a latent image is transferred onto a transfer sheet and fixed thereon to provide a copy.
One transfer and fixing technique used in such an electrophotographic apparatus comprises the steps of disposing a transfer sheet in superimposed relationship with a toner image on a photosensitive member, effecting a corona discharge of the opposite polarity from that of the toner from behind the transfer sheet to transfer the toner image onto the sheet, and fixing the transferred toner image on the sheet under heat and/or pressure. Another technique comprises the steps of disposing a transfer sheet in superimposed relationship with the toner image on the photosensitive member, applying a member such as a roller which is electrically energized to the opposite polarity from that of the toner to the rear surface of the sheet to effect the transfer of the toner image onto the sheet, and fixing the transferred toner image to the sheet under heat and/or pressure. However, these techniques, though extensively used in conventional electrophotographic apparatus, suffer from the susceptibility of the surface of the photosensitive member to damage since the transfer sheet is directly brought into contact with the surface when transferring the toner image onto the sheet. Also, the surface of the photosensitive member may be subject to damage as a result of a jamming of the sheet which may become entangled with a transfer charger. In addition, the separation of the transfer sheet from the surface of the photosensitive member relies on the use of electrostatic means such as a.c. corona discharge or mechanical means such as claws or separator belt, both of which leaves much to be improved, since they give rise to the likelihood that the transfer sheet may be jammed or entangled to the photosensitive member. When separating the transfer sheet from the photosensitive member, the transferred toner image may be disrupted or may be partly lost, or a non-uniformity may occur in the effect of the transfer. As an alternative, a toner image on the photosensitive member may be temporarily transferred onto an intermediate transfer material, from which the toner image may again be transferred onto a transfer sheet under heat and/or pressure, as exemplified in U.S. Pat. No. 3,951,276. However, such technique suffers from the quality of the transfer which remains unsatisfactory.